Human DNase I is a member of the mammalian DNase I family (EC 3.1.21.1). DNase I belongs to the class of Mg2+ and Ca2+ dependent endonucleases, whose hydrolytic activity depends on the presence of bivalent metals. Magnesium ion is involved in electrophilic catalysis of the phosphodiester bond cleavage, whereas Ca2+ maintains optimal enzyme conformation. DNase I cleaves DNA preferentially at phosphodiester linkages adjacent to a pyrimidine nucleotide, yielding 5′-phosphate-terminated polynucleotides with a free hydroxyl group on position 3′, on average producing tetranucleotides. It acts on single-stranded DNA, double-stranded DNA, and chromatin.
The principal therapeutic use of human DNase has been to reduce the viscoelasticity of pulmonary secretions (including mucus) in such diseases as pneumonia and cystic fibrosis (CF), thereby aiding in the clearing of respiratory airways. Mucus also contributes to the morbidity of chronic bronchitis, asthmatic bronchitis, bronchiectasis, emphysema, acute and chronic sinusitis, and even the common cold. DNase I is effective in reducing the viscoelasticity of pulmonary secretions and fluids by hydrolyzing high-molecular-weight DNA present in pulmonary secretions and fluids. DNase has also been proposed for non-pulmonary disorders, for example, treatment of male infertility and uterine disorders (see US 2007/0259367), inhibition of metastatic growth (see U.S. Pat. No. 7,612,032) and for treatment of sepsis and viral, bacterial, fungal and protozoan infections.
DNA encoding human DNase I was isolated and sequenced, and expressed in recombinant host cells, thereby enabling the production of human DNase in commercially useful quantities. Recombinant human DNase (rhDNase) (e.g. dornase alfa; Pulmozyme®, Genentech, Calif.), expressed in Chinese hamster ovary (CHO) cells, has been found to be clinically effective for CF.
Recombinant human DNase (rhDNase) (e.g. dornase alfa; Pulmozyme®, Genentech, Calif.) was approved for clinical use by the FDA in 1994, and additional human clinical trials with recombinant human DNase I are currently in progress for CF (see NCT01155752; NCT0017998; NCT00117208 and NCT00204685) and other chronic, respiratory diseases such as atelectasis (see NCT01095276 and NCT00671323) and Sjogren's Syndrome. In general, safety and efficacy of the rhDNase has been demonstrated. Pulmozyme® is provided as a liquid protein formulation ready for use in nebulizer systems.
In addition to nebulizer systems, pulmonary administration of drugs and other pharmaceuticals can be accomplished by provision of an inhalable solution formulated for inhalation by means of suitable liquid-based inhalers known as metered dosage inhalers.